1. Field of the Invention
The present invention relates to a receiver of analogue video signal having means for analogue video signal conversion and a method for control of display of video frames, used in digital decoders/receivers of television signal, in which the signal is received in an analogue form, and then, after conversion into a digital signal, it is processed in the decoder/receiver (e.g. OSD ‘On-Screen Display’ functions are applied). Next it is converted to an analogue format, which is transmitted to a receiver, for example a TV set.
2. Brief Description of the Background of the Invention Including Prior Art
The methods of controlling display of video signal frames, known from the prior art, can be divided into three groups. The first group uses a single frame buffer, and the input of video signal (refresh frequency timer) is not synchronized with the output. The drawback of this solution are the interferences, which appear during the displaying of video frames. They appear, for instance, as a shift of the top part of the picture in relation to the bottom part.
The second solution consists in applying a single frame buffer and synchronization of the input signal timers with the output signal. Although interferences occurring in the first method do not appear here, it is still necessary to synchronize the timers. Moreover, there appear problems related to switching among input signals with different synchronization frequencies/phases.
The third method, called “back buffering” or “double buffering”, requires two frame buffers. Data are fetched into the first one, and next they are copied to the second one. The contents of the second buffer are displayed. A disadvantage of this solution is the necessity of copying large amounts of data.
The U.S. Pat. No. 5,446,496 presents a solution, in which the frequency of video frames is converted. The output frequency in this solution must be lower than the input frequency. Moreover, a single frame buffer is used for the conversion, which—during considerable discrepancies between input and output frame frequencies—may lead to the loss of many video signal frames. This is due to the fact, that the currently displayed data cannot be overwritten.